How to control an hybrid scooter : electric mode - Gasoline mode

I am building a Parallel Hybrid Scooter using Kelly Controll components (include hub motor)! Now I left the gasoline engine, but I want to controll it using the same Throttle Hall 0-5V Twist Grip that I bought from Kelly. I need to control the throttle body with an electric motor (stepper motor or brushless, or dc) that I have to connect with the Throttle Hall 0-5V. The scooter is a Yamaha Majesty 250cc , 1998. Which motor can I use?
Is there somebody that can help me?